Anionic tensides dominate the field of emulsifying agents in the technical preparation of polymer dispersions. In addition to alkyl sulfates, alkyl polyalkylene ether glycol sulfates and alkyl benzene sulfonates, the main substances used today are mainly alkaryl polyalkylene ether glycol sulfates, and sulfosuccinates of natural and synthetic alcohol polyalkylene ether glycols or alkylphenol ethoxylates.
The preparation of such emulsifying agents is known and is described in detail in the scientific literature and especially also in patent specifications. Reference is made in this respect to Lindner, "Tenside, Textilhilfsmittel, Waschrohstoffe," Stuttgart, Germany, Vol. 1, 1964, especially pages 619-624, 636-643, 673-678 and 768-787; as well as to German Pat. DE-PS No. 834,245; Belgian Pat. BE-PS No. 680,629; U.S. Pat. No. 1,970,578; French Pat. FR-PS No. 1,079,974; U.S. Pat. Nos. 2,416,254, 2,489,026, 2,510,008 and 2,758,977.
In this context, emulsifying agents of the mentioned type usually are offered commercially in the form of dilute aqueous solutions. Highly concentrated mixtures can be prepared only with the addition of up to 20% of lower alkanols such as ethanol or isopropanol. The presence of organic solvents, for example, the mentioned alcohols, is not always desirable in polymer dispersions, however, for reasons of application technology. In addition, the presence of these alcohols present a considerable safety risk during the preparation of the emulsifying agents as well as during transporting, storage and use. In addition, it is known that even slight shifts in the ratio of water to alcohol can lead to undesirable sedimentation in such concentrates.
In addition thereto, the expert skilled in the art knows that upon the dilution of aqueous tenside concentrates containing no alcohols, the mixture frequently passes through the phase of a thick gel that can no longer be pumped. This leads to considerable difficulties in the operation. For example, it frequently is no simple matter to bring lumps of gel, once they have formed, back into solution. The valves of feeding vessels can be clogged with them and variations in concentration during dosing may occur. Finally, the diluting of such aqueous tenside pastes is a very time-consuming process for the reasons mentioned above.
The preparation of highly concentrated alkyl polyalkylene ether glycol sulfates that can be pumped is also known to present a problem that remains difficult to solve. Alkyl polyalkylene ether glycol sulfates, also called alkyl ether sulfates are especially sulfates of alkoxylated nonaromatic alcohols with 8 to 24 carbon atoms, particularly 8 to 18 carbon atoms. Alcohols of this type can be obtained from naturally occurring starting materials, such as coconut oil or palm oil, or they are synthetic materials, such as known Ziegler alcohols or oxo-alcohols. The nonaromatic alcohols with saturated or unsaturated, optionally also branched, radicals of the mentioned type, are first alkoxylated with lower alkylene oxides, especially with ethylene oxide and/or with propylene oxide, subsequently sulfated and then converted into the respective water-soluble salts. Such products are useful for the preparation of detergents.
Detergents of this type are used for many purposes, for example, in liquid cleaning agents, foam baths and shampoos.
Aqueous solutions with a relatively low content of alkyl ether sulfate, for example, with a content of about 10% by weight of wash-active substance (WAS), exhibit the special property of this class of detergents, that is, of being thickened again by the addition of neutral salts, such as NaCl or Na.sub.2 SO.sub.4. This ability of the class of detergents in question frequently is made use of in practice.
However, another characteristic with respect to rheological behavior of respective tenside concentrates causes grave problems for practical applications. Highly concentrated aqueous tenside concentrates with a WAS content of 50% by weight or more, for example, have the consistency of a thick gel or a corresponding paste and cannot be pumped. Attempts to thin out this gel with water do not reduce the thickness, as might be expected, but initially result in its increase. It is understandable that this leads to considerable problems for the use of the material.
Several recommendations have been made to overcome these difficulties. For example, The German Published Application DE-OS No. 22 51 405 describes the use of certain salts of carboxylic acids. Particularly the salts of hydroxycarboxylic acids, such as sodium citrate, are recommended. According to DE-OS No. 23 05 554, aromatic sulfonic acids and their salts are suitable for the same purpose. According to DE-OS No. 23 26 006, sulfonic acids or sulfates or the respective water-soluble salts of saturated or unsaturated aliphatic hydrocarbon radicals with 1 to 6 carbon atoms can be used as viscosity regulators. However, all these recommendations limit themselves to the group of linear alkyl polyglycol ether sulfates and their use as detergent tensides.